How can I send Perl output to a both STDOUT and a variable?

Question

I would like to send the output from a command to both STDOUT and to a variable. I want to combine:

my $var = `some command` ;   
system( 'some command' ) ;

Tee is a step in the right direction but this sends it to a file rather than to a variable. I guess I could then read the file but it would be simpler to get it straight there.

Answer 1

Does the output to both streams have be simultaneous?

If not, you could do:

my $var = 'cmd'
my $output = `$cmd`
print STDOUT $output

or for a safer version, which doesn't involve invoking a subshell, and prints to STDOUT a line at a time:

sub backtick(@)
{
    my $pid = open(KID, '-|');
    die "fork: $!" unless defined($pid);
    if ($pid) {
        my $output;
        while (<KID>) {
            print STDOUT $_;
            $output .= $_; # could be improved...
        }
        close(KID);
        return $output;
    } else {
        exec @_;
    }
}

my @cmd = ('/bin/ls', '-l');
my $output = backtick(@cmd);

Answer 2

You want Capture::Tiny

use Capture::Tiny 'tee';
my $output = tee { system( "some command" ) };

I wrote it to replace Tee and about 20 other modules that do some sort of capturing but are flawed in one way or another.

-- xdg (aka dagolden)

Answer 3

Perhaps my answer here can help you: How can I hook into Perl's print?

Answer 4

You could use the IO::String module to select() STDOUT to a string and then call system() to run the command. You can collect the output from the IO::String handle. This effectively does what the backtick syntax does.

So to gather command output realtime, run the system() command asynchronously through fork() or some other means and poll the handle for updates.

EDIT: Per OP, it turns out this approach does not work. select() doesn't affect system() calls.

Also, IO::String has been replaced with new open() syntax since Perl 5.8 that does the same function.

Answer 5

You can do this through a file handle as well. Not as elegant as some solutions, but it would likely work. Something along the lines of:

my $foo;
open(READ, "env ps |");
while (<READ>) {
    print;
    $foo .= $_;
}
print $foo;
close(READ);

Answer 6

my $output = system("your command | tee /dev/tty");

Worked for me!!

Answer 7

    package Logger ; 
    # docs at the end ... 
    use lib '.' ; use strict ; use warnings ; use Carp qw(cluck); 

    our ( $MyBareName  , $LibDir , $RunDir ) = () ; 

    BEGIN {     


        $RunDir = '' ; 
        $0 =~ m/^(.*)(\\|\/)(.*)\.([a-z]*)/; 
        $RunDir = $1 if defined $1 ; 
        push ( @INC , $RunDir) ;    
        #debug print join ( ' ' , @INC ) ; 

    } #eof sub

    use Timer ; use FileHandler ; 

    # the hash holding the vars 
    our $confHolder = () ; 

    # ===============================================================
    # START OO


    # the constructor 
    sub new {

        my $self = shift;
        #get the has containing all the settings
        $confHolder = ${ shift @_ } ;                                           
        # Set the defaults ...
        Initialize () ;     
        return bless({}, $self);
    } #eof new 


    BEGIN { 

            # strip the remote path and keep the bare name
            $0=~m/^(.*)(\\|\/)(.*)\.([a-z]*)/; 
            my ( $MyBareName , $RunDir ) = () ; 
            $MyBareName = $3; 
            $RunDir= $1 ; 

            push ( @INC,$RunDir ) ; 

    } #eof BEGIN


    sub AUTOLOAD {

        my $self = shift ; 
        no strict 'refs'; 
            my $name = our $AUTOLOAD;
            *$AUTOLOAD = sub { 
        my $msg = "BOOM! BOOM! BOOM! \n RunTime Error !!!\nUndefined Function $name(@_)\n" ;
        print "$self , $msg";
            };
            goto &$AUTOLOAD;    # Restart the new routine.
    }   

    sub DESTROY {

        my $self = shift;
        #debug print "the DESTRUCTOR is called  \n" ; 
        return ; 
    } 

    END { 

        close(STDOUT) || die "can't close STDOUT: $! \n\n"  ; 
        close(STDERR) || die "can't close STDERR: $! \n\n" ; 
    }

    # STOP OO
    # =============================================================================

    sub Initialize { 

        $confHolder = { Foo => 'Bar' ,   } unless ( $confHolder ) ; 
        # if the log dir does not exist create it 
        my $LogDir = '' ; 
        $LogDir = $confHolder->{'LogDir'} ; 

        # create the log file in the current directory if it is not specified 
        unless ( defined ( $LogDir )) {
        $LogDir = $RunDir  ; 
        }

    use File::Path qw(mkpath);

        if( defined ($LogDir) &&  !-d "$LogDir" ) {  
                mkpath("$LogDir") || 
                cluck ( " Cannot create the \$LogDir : $LogDir $! !!! "  ) ; 
        }

        # START set default value if value not specified =========================
        # Full debugging ....
            $confHolder->{'LogLevel'} = 4   
                    unless ( defined ( $confHolder->{'LogLevel'} ) )  ; 

            $confHolder->{'PrintErrorMsgs'} = 1     
                    unless ( defined ( $confHolder->{'PrintErrorMsgs'} ) )  ; 

            $confHolder->{'PrintDebugMsgs'} = 1 
                    unless ( defined ($confHolder->{'PrintDebugMsgs'})) ; 

            $confHolder->{'PrintTraceMsgs'} = 1 
                    unless ( defined ( $confHolder->{'PrintTraceMsgs'} )) ; 

            $confHolder->{'PrintWarningMsgs'} = 1   
                    unless ( defined ( $confHolder->{'PrintWarningMsgs'} ) )  ; 

            $confHolder->{'LogMsgs'} = 1
                    unless ( defined ( $confHolder->{'LogMsgs'} ) )  ; 

            $confHolder->{'LogTimeToTextSeparator'} = '---'
                    unless ( defined ( $confHolder->{'LogTimeToTextSeparator'} ) )  ; 


        #
        # STOP set default value if value not specified =========================

    } #eof sub Initialize

    # =============================================================================
    # START functions


    # logs an warning message
    sub LogErrorMsg {

        my $self = shift ; 
        my $msg = "@_" ; 
        my $msgType = "ERROR" ; 

        # Do not print anything if the PrintWarningMsgs = 0 
        return if ( $confHolder->{'LogMsgs'} == 0 )     ; 

        # Do not print anything if the PrintWarningMsgs = 0 
        return if ( $confHolder->{'PrintErrorMsgs'} == 0 )  ; 

        $self->LogMsg( $msgType , "$msg" ) if ( $confHolder->{'PrintErrorMsgs'} == 1 ) ; 

    } #eof sub

    # logs an warning message
    sub LogWarningMsg {

        my $self = shift ; 
        my $msg = "@_" ; 
        my $msgType = 'WARNING' ; 

        # Do not print anything if the PrintWarningMsgs = 0 
        return if ( $confHolder->{'LogMsgs'} == 0 )     ; 

        # Do not print anything if the PrintWarningMsgs = 0 
        return if ( $confHolder->{'PrintWarningMsgs'} == 0 )    ; 

        $self->LogMsg( $msgType , "$msg" ) if ( $confHolder->{'PrintWarningMsgs'} == 1 ) ;  

    } #eof sub



    # logs an info message
    sub LogInfoMsg {

        my $self = shift ; 
        my $msg = "@_" ; 
        my $msgType = 'INFO' ; 

        # Do not print anything if the PrintWarningMsgs = 0 
        return if ( $confHolder->{'LogMsgs'} == 0 )     ; 

        # Do not print anything if the PrintWarningMsgs = 0 
        return if ( $confHolder->{'PrintInfoMsgs'} == 0 )   ; 

        $self->LogMsg( $msgType , "$msg" ) if ( $confHolder->{'PrintInfoMsgs'} == 1 ) ;  

    } #eof sub

    # logs an trace message
    sub LogTraceMsg {

        my $self = shift ; 
        my $msg = "@_"  ; 
        my $msgType = 'TRACE' ; 
        my ($package, $filename, $line) = caller();     


        # Do not print anything if the PrintDebugMsgs = 0 
        return  if ( $confHolder->{'PrintTraceMsgs'} == 0 )      ; 

        $msg = "$msg : FROM Package: $package  FileName: $filename Line: $line  "  ; 

        # Do not print anything if the PrintWarningMsgs = 0 
        return if ( $confHolder->{'LogMsgs'} == 0 )     ; 

        # Do not print anything if the PrintWarningMsgs = 0 
        return if ( $confHolder->{'PrintTraceMsgs'} == 0 )  ; 

        $self->LogMsg( $msgType , "$msg" ) if ( $confHolder->{'PrintTraceMsgs'} == 1 ) ;  

    } #eof sub

    # logs an Debug message
    sub LogDebugMsg {

        my $self = shift ; 
        my $msg = "@_" ; 
        my $msgType = 'DEBUG' ; 

        # Do not print anything if the PrintWarningMsgs = 0 
        return if ( $confHolder->{'LogMsgs'} == 0 )     ; 

        # Do not print anything if the PrintWarningMsgs = 0 
        return if ( $confHolder->{'PrintDebugMsgs'} == 0 )  ; 

        $self->LogMsg( $msgType , "$msg" ) if ( $confHolder->{'PrintDebugMsgs'} == 1 ) ;  

    } #eof sub

    sub GetLogFile {

            my $self = shift ; 
            #debug print "The log file is " . $confHolder->{ 'LogFile' } ;  
            my $LogFile = $confHolder->{ 'LogFile' } ; 

            #if the log file is not defined we create one 
            unless  ( $confHolder->{ 'LogFile' } ) { 

                $LogFile = "$0.log"  ;

            }

            return $LogFile ; 
    } #eof sub 

    sub BuildMsg { 

    my $self = shift ; 
    my $msgType = shift ; 

    my $objTimer= new Timer(); 
    my $HumanReadableTime = $objTimer->GetHumanReadableTime(); 
    my $LogTimeToTextSeparator = $confHolder->{'LogTimeToTextSeparator'} ; 

    my $msg = () ; 

        # PRINT TO STDOUT if 
        if (                $msgType eq 'WARNING' 
                    ||      $msgType eq 'INFO' 
                    ||      $msgType eq 'DEBUG' 
                    ||      $msgType eq 'TRACE'                     )   {

            $msg = " $HumanReadableTime $LogTimeToTextSeparator $msgType : @_ \n" ; 

        }
        elsif ( $msgType eq 'ERROR' ) {

            $msg = " $HumanReadableTime $LogTimeToTextSeparator $msgType : @_ \n" ; 

        }
        else {
            $msg = " $HumanReadableTime $LogTimeToTextSeparator $msgType @_ \n" ; 
        }



        return $msg ; 
    } #eof sub BuildMsg

    sub LogMsg { 

    my $self = shift ; 
    my $msgType = shift ; 

    my $msg = $self->BuildMsg ( $msgType , @_ ) ; 
    my $LogFile = $self -> GetLogFile();                            


    # Do not print anything if the LogLevel = 0 
    return              if ( $confHolder->{'LogLevel'} == 0 ) ; 

        # PRINT TO STDOUT if 
        if (                
                                $confHolder->{'PrintMsgs'} == 1 
                    ||      $confHolder->{'PrintInfoMsgs'} == 1 
                    ||      $confHolder->{'PrintDebugMsgs'} == 1 
                    ||      $confHolder->{'PrintTraceMsgs'} == 1 
                    )   {

            print STDOUT $msg ; 
        }

        elsif ( $confHolder->{'PrintErrorMsgs'}  ) {

            print STDERR $msg ; 
        }


        if ( $confHolder->{'LogToFile'} == 1 )  {   

            my $LogFile = $self -> GetLogFile();
            my $objFileHandler = new FileHandler();

            $objFileHandler->AppendToFile( $LogFile , "$msg"  );

        } #eof if

        #TODO: ADD DB LOGGING

    } #eof LogMsg



    # STOP functions
    # =============================================================================


    1;

    __END__



    =head1 NAME

    Logger 

    =head1 SYNOPSIS

    use Logger  ; 


    =head1 DESCRIPTION

    Provide a simple interface for dynamic logging. This is part of the bigger Morphus tool : google code morphus
    Prints the following type of output : 

    2011.06.11-13:33:11 --- this is a simple message  
    2011.06.11-13:33:11 --- ERROR : This is an error message  
    2011.06.11-13:33:11 --- WARNING : This is a warning message  
    2011.06.11-13:33:11 --- INFO : This is a info message  
    2011.06.11-13:33:11 --- DEBUG : This is a debug message  
    2011.06.11-13:33:11 --- TRACE : This is a trace message  : FROM Package: Morphus  
    FileName: E:\Perl\sfw\morphus\morphus.0.5.0.dev.ysg\sfw\perl\morphus.pl Line: 52   

    =head2 EXPORT


    =head1 SEE ALSO

    perldoc perlvars

    No mailing list for this module


    =head1 AUTHOR

    yordan.georgiev@gmail.com

    =head1 COPYRIGHT AND LICENSE

    Copyright (C) 2011 Yordan Georgiev

    This library is free software; you can redistribute it and/or modify
    it under the same terms as Perl itself, either Perl version 5.8.1 or,
    at your option, any later version of Perl 5 you may have available.



    VersionHistory: 
    1.4.0 --- 2011.06.11 --- ysg --- Separated actions of building and printing msgs. Total refactoring. Beta . 
    1.3.0 --- 2011.06.09 --- ysg --- Added Initialize 
    1.2.0 --- 2011.06.07 --- ysg --- Added LogInfoErrorMsg print both to all possible
    1.1.4 --- ysg --- added default values if conf values are not set 
    1.0.0 ---  ysg --- Create basic methods 
    1.0.0 ---  ysg --- Stolen shamelessly from several places of the Perl monks ...

    =cut

Answer 8

Send the output from the Tee module to /dev/stdout (or /dev/fd/1 ).